The present invention relates to a semiconductor laser device, and in particular, it relates to a multi-beam semiconductor laser device for generating plural numbers of laser beams therefrom.
Accompanying wide distribution of PPC (Plain Paper Copier), a requirement of high-speed in a printing speed increases for a laser printer, and in particular, a demand rises up, rapidly, for the multi-beam semiconductor laser device for generating plural numbers of laser beams therefrom. With such multi-beam semiconductor laser device, since it has light emitting portions, which are aligned in one-dimensional or two-dimensional manner, a number of scanning beams can be increased, and thereby having an advantage of enabling a high-speed printing.
By the way, in the general structure of such multi-beam semiconductor laser device, as is already known in the following Patent Document 1, for example, a plural number of laser elements are formed on a semiconductor substrate, while providing a region (e.g., a groove) for separation, between the laser elements, for each; thereby forming the light emitting portions, which are aligned in one-dimensional or two-dimensional manner. However, according to this Patent Document 1, for the purpose of obtaining multi-beam semiconductor laser, being uniform in the characteristics thereof, such as, wavelength of emission light, a luminous efficiency, an output for each laser element, etc., there is disclosed that the laser elements, which are formed in an outside region of the substrate, are used as dummy laser elements (i.e., supporting portions), which do not emit the lights when being used.
Also, with such multi-beam semiconductor laser device as was mentioned above, since the amount of heat generation in the laser devise goes up accompanying with an increase of a number of light emitting points on one (1) piece of the semiconductor substrate, it is necessary to improve heat radiation efficiency thereof. However, in the following Patent Document 2, there is provided the structure of a semiconductor laser device having laser elements emitting the laser lights having different wavelengths, wherein, in particular for achieving an improvement of the heat radiation efficiency thereof, a light emitting point of the laser elements, emitting a laser light having the shortest wavelength, is substantially positioned on a center line of the substrate when seeing it in a direction parallel with a main surface of that substrate, within a surface perpendicular to an optical axis of that laser element.
In addition thereto, with such multi-beam semiconductor laser device as was mentioned above, because of the requirements of suppressing relative differences of the beam characteristics from each laser element, such as, a wavelength, a polarizing angle, a luminous efficiency, an optical output, etc., for example, therefore it is an important problem to be dissolved; e.g., reducing thermal stress when being mounted, and thereby lowering the relative difference of strain applied onto the light emitting portions. However, with the well-known prior documents, it is already known that the polarization direction of a beam rotates in proportion to the shear strain generating within a semiconductor layer, according to the following Non-Patent Document 1.